Fluid-operated braking systems have long been utilized to control the movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles such as trucks, which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles in combination with the high speeds at which they travel requires a braking system which responds rapidly with substantial braking power. One system component which is instrumental in the operation of air brake systems is the brake actuator, which provides the force necessary for braking a vehicle.
In a typical diaphragm spring brake actuator, the brakes may be applied in a number of ways. For normal braking operation, compressed air is introduced into the brake chamber, which coacts with a diaphragm, typically an elastomeric diaphragm, and a push rod to apply the brakes. For emergency and/or parking brake applications, a barrel-shaped power spring stores potential energy and exerts the large force required for braking in case of air pressure failure. During normal driving operation, air pressure compresses the power spring and maintains it in its brake release position. When the air is exhausted, the power spring expands coacting with the diaphragm and push rod and thereby applies the brakes in case of failure of the system air pressure or exhaustion of compressed air while the vehicle is not in operation or is parked.
The power spring is positioned in a spring chamber, which is typically formed by clamping an elastomeric diaphragm between a head (sometimes also known as a spring housing or spring chamber) and a flange case (sometimes known as an adaptor). The power spring is compressed within the spring chamber between the head and the diaphragm. The power spring has a high spring constant and is normally compressed to a height of less than 3 inches from an original uncompressed height of from 9 to 12 inches. The power spring, therefore, stores a substantial amount of potential energy, usually exerting a force on the head of about 2,000 to 3,000 pounds.
It is undesirable to unnecessarily expose the power spring to corrosive elements such as dirt and moisture, because due to the large forces involved, the power spring is subject to failure. As the power spring provides emergency breaking for the vehicle if the air system malfunctions, failure or breakage of the power spring because of for instance, corrosion, could be catastrophic resulting in a complete failure of the vehicle braking system.
Typically air drawn from the atmosphere to be utilized with air brake assemblies is passed through an air filter/drier after being compressed. This allows the air compressor to supply clean, dry air to the braking system. However, the vent air in the spring brake chamber itself is generally drawn directly from the atmosphere as compressed air is not utilized to supply vent air when one actuates the emergency or parking brake. This is undesirable as stated above because dirt and moisture may then be drawn into the spring brake chamber, which may corrode the power spring.
Various systems have sought to prevent the introduction of dirt and moisture into the spring cavity. For instance, U.S. Pat. Nos. 3,736,842 and 3,800,668 both to Valentine (“the '842 patent” and “the '668 patent”) disclose a breathing system for spring brake actuators that allows the flow of air from within the actuator assembly to and from the spring cavity so that dirt and moisture present in the outside air is not delivered to the spring cavity. However, both the '842 patent and the '668 patent disclose a systems that utilize an O-ring seal for sealing between the control cavity and the service chamber. As the brake assembly laterally reciprocates between the parking break engaged and disengaged positions, fluid communication is selectively made between the spring cavity and the control cavity or between the spring cavity and the service chamber. The lateral reciprocation of the brake assembly will cause wear to the O-ring seal such that bleeding of pressurized air between the control cavity and service chamber results in unnecessary loss of compressed air in the system. This in turn will cause unnecessary cycling of the system to make up for the constant air losses.
Another disadvantage of the systems taught in both the '842 patent and the '668 patent is that the brake assembly oscillates once the internal breathing valve is displaced to the opened position. This too will cause unnecessary cycling of the system. Still another disadvantage of the systems taught in both the '842 patent and the '668 patent is that the housing for the spring cavity must be sized to withstand the large pressures introduced therein from the control cavity. In addition, the added pressure to the spring cavity increases the speed and likelihood that the spring brake will be applied immediately if system emergency/parking air is lost.
Another system that has attempted to deal with this problem is U.S. Pat. No. 4,890,540 to Mullins (“the '540 patent”). The '540 patent discloses a system having a plurality of breather holes provided in the housing section of the power spring. The breather holes are located in the upper hemisphere of the housing to minimize the amount of dust and dirt that enters the housing. This system however, does not prevent moisture from entering the housing section of the power spring and will also not prevent contaminates from entering. At best, the system will simply slow the amount of contaminates that enter the housing.
Still another system is disclosed in U.S. Pat. No. 6,006,651 to Pierce et al. (“the '651 patent”). The '651 patent provides a gas permeable filter element over opening in the housing so that air entering the service brake inner chamber from the atmosphere will be substantially free of contaminates. However, this system does not prevent the introduction of moisture into the housing section of the power spring. While the '651 patent claims that the filters will prevent the introduction of contaminates, these filters, being so close to the roadway, will constantly need to be changed as dirt is drawn into them resulting in a system that requires much more maintenance and therefore downtime for the vehicle.
Yet another system is disclosed in U.S. Pat. No. 4,889,037 to Goral et al. (“the '037 patent”). The '037 patent provides for fluid communication between the power spring chamber and breather chamber which in turn is vented to atmosphere. This connection is provided so that solids and fluid that enter the breather chamber will not cause problems within the power spring chamber. However, this system still vents the power spring chamber to atmosphere, simply making the path a little longer. Contaminates will build up in the breather chamber, but this will not eliminate build up of contaminates in the power spring chamber. In addition, this system will not prevent moisture from entering the power spring chamber.
In still another system is disclosed in U.S. Pat. No. 5,937,733 to Stojic (“the '733 patent”). The '733 patent, like the '651 patent provides a filter assembly that covers holes in the power spring chamber. The filter assembly is provided for filtering air drawn from atmosphere into the power spring chamber. This system suffers from the same problems as the '651 patent, namely it does not prevent moisture from entering and will require a large amount of maintenance to keep the filters clean and functional.
Therefore, what is desired is to provide a braking system that minimizes the amount of dirt and moisture that is introduced into the power spring chamber.
It is further desired to provide a braking system that provides dry, filtered air to the power spring chamber.
It is still further desired to provide a braking system that minimizes air losses.
It is yet further desired to provide a braking system that facilitates the fluid communication of air from the service side of the brake actuator to the power spring chamber.
It is still further desired to provide a braking system that reduces the stress on the power spring.